The present invention relates to a planar type optical scanning apparatus that is manufactured using semiconductor manufacturing technology, and in particular to a technique for miniaturizing and reducing the cost of planar type optical scanning apparatus.
The present inventor has previously proposed a very small size planar type optical scanning apparatus which is manufactured by micro machining technology in which semiconductor manufacturing technology is applied, for example a planar type mirror galvanometer (refer to Japanese Unexamined Patent Publication Nos. 7-175005, 7-218857 and 8-322227).
A description of the principle of operation of this planar type optical scanning apparatus is given below.
The planar type optical scanning apparatus comprises a silicon substrate on which is integrally formed a planar movable portion, and an axial support portion of a torsion bar construction, for axially supporting the movable portion so as to be able to swing in a central location of the movable portion, relative to the silicon substrate. A mirror is provided in the center of the movable portion, and a drive coil of thin copper film, for generating a magnetic field by means of a current, is provided at the periphery thereof. Moreover, static magnetic field generating devices, such as pairs of permanent magnets, are provided at the periphery of the movable portion so that the resultant static magnetic fields act on the drive coil portion located on opposite sides of the movable portion, those opposite sides being parallel to the axial direction of the axial support portion. With the abovementioned patent applications, pairs of permanent magnets are respectively located above and below the opposite side portions of the movable portion, the construction being such that the static magnetic fields generated between the pairs of permanent magnets intersect the drive coil in predetermined directions.
The optical scanning apparatus with such a construction drives the movable portion by the interaction of a magnetic field generated by passing a current through the drive coil, and a static magnetic field generated by the static magnetic field generating devices.
That is to say, a static magnetic field is formed by means of the permanent magnets on opposite sides of the movable portion, in a direction so as to intersect the drive coil along the planar face of the movable portion. When a current flows in the drive coil positioned in this static magnetic field, a magnetic force acts in a direction according to Fleming""s left hand rule for current, magnetic flux density and force, on the opposite sides of the movable portion in proportion to the current density and magnetic flux density of the drive coil, as represented by the following equation (1), so that the movable portion is rotated.
F=ixc3x97Bxe2x80x83xe2x80x83(1)
where F is the magnetic force, i is the current flowing in the drive coil, and B is the magnetic flux density.
The axial support portion is twisted with the rotation of the movable portion, producing a spring reaction force, so that the movable portion rotates to a position where the magnetic force and the spring reaction force are in equilibrium. The angle of rotation of the movable portion is proportional to the current flowing in the drive coil, and hence the rotation angle of the movable portion can be controlled by controlling the current flowing in the drive coil. Consequently, the direction of reflection of light, such as a laser beam incident on the mirror in a plane perpendicular to the axis of the axial support portion, can be freely controlled. Hence scanning of light such as laser scanning is possible by cyclical operation to continuously change the mirror displacement angle.
Since this optical scanning apparatus is produced using single crystal silicon, which is light, strong, and capable of being batch processed, mass production with consistent quality is possible.
In the case where a large number of chips are produced by batch processing of semiconductor wafers, the cost of one wafer is the same wherever the same process is used. Consequently, if the number of chips that can be produced on one wafer is increased, in other words if the chips are further miniaturized, the cost is reduced accordingly.
However, with conventional planar type optical scanning apparatus, when mounting on a package substrate for mounting, to make it easy to wire the drive coil and external electrodes, a mirror 2 and a drive coil 3 are formed on the same face (surface side) of the movable portion 1 shown in FIG. 10(A) so that the drive coil electrode terminals are positioned on the surface side of the semiconductor substrate. In this case, if the mirror 2 and the drive coil 3 are stacked, the surface becomes uneven, and hence the light reflection characteristics become irregular. Therefore the drive coil 3 is arranged around the mirror 2 shown in the figure so that the mirror 2 and the drive coil 3 do not overlap. As a result, the movable portion 1 requires not only a mirror formation area but also a drive coil formation area, and there is a limit to miniaturization of the movable portion. FIG. 10(B) shows the rear surface side of the optical scanning apparatus. In the figures, 4 denotes the semiconductor substrate, 5A and 5B denote axial support portions of a torsion bar structure for axially supporting the movable portion 1 so as to swing relative to the semiconductor substrate 4, and 6 denotes the electrode terminal of the drive coil 3.
As a planar type optical scanning apparatus, in addition to the aforementioned conventional technique, there are those disclosed for example in Japanese Unexamined Patent Publication Nos. 60-107017, 4-211218, and U.S. Pat. No. 4,421,381. However, with all of these, the mirror and the drive coil are provided on the same face side.
The present invention takes into consideration the above situation with the object of providing a planar type optical scanning apparatus that, by arranging the mirror on one face of the movable portion and the drive coil on the other face, enables further miniaturization, and in turn can achieve cost reduction.
Accordingly, with a planar type optical scanning apparatus of a first aspect of the present invention, a movable portion and an axial support portion for axially supporting the movable portion so as to be able to swing, are integrally formed on a semiconductor substrate, a mirror is provided on the surface side of the movable portion, a drive coil is provided on the rear face side of the movable portion, and there is provided a magnetic field generation device for applying a static magnetic field to the drive coil, the construction being such that the movable portion is driven by a magnetic force generated by passing a current through the drive coil.
With such a construction, since the mirror and the drive coil are formed on the surface side of the movable portion and the rear face side of the movable portion respectively, compared with conventional apparatus, an optical scanning apparatus having the same mirror area can be miniaturized by the size of the formation area of the drive coil.
With a mounting structure of a second aspect of the present invention for mounting the planar type optical scanning apparatus of the present invention on a mounting substrate, a cavity for allowing swinging movement of the movable portion of the optical scanning apparatus, and a conductive pattern are provided in an optical scanning apparatus fixing region of the mounting substrate, the construction being such that when the optical scanning apparatus is fitted in the fixing region, a drive coil electrode terminal provided on the rear face of the semiconductor substrate of the optical scanning apparatus, and the conductive pattern make contact.
With such a construction, when the optical scanning apparatus is fitted on the mounting substrate, since the drive coil electrode terminals of the optical scanning apparatus side can be electrically connected to terminal pins of the mounting substrate via the conductive patterns, even if the drive coil is formed on the rear face side, the optical scanning apparatus can be easily mounted on the mounting substrate.
In a third aspect, the construction of the mounting substrate is such that terminal pins for feeding out electrodes that are electrically connected to the conductive pattern are fixed at the periphery of the fixing region. Hence it is possible to connect to the outside by the terminal pins using a one-touch operation.
In a fourth aspect, the construction is such that solder surfaces are formed on the conductive pattern and the drive coil electrode terminal, respectively, and the two solder surfaces are thermo compression bonded to fix the optical scanning apparatus to the fixing region of the mounting substrate. Hence it is possible to secure the optical scanning apparatus and connect the electrode terminals at the same time.
With a mounting structure of a fifth aspect of the present invention for mounting the planar type optical scanning apparatus of the present invention on a mounting substrate, the structure has an auxiliary substrate provided with a cavity for allowing swinging movement of a movable portion of the optical scanning apparatus, and a conductive pattern at least at the periphery of the cavity of the rear face side, the construction being such that the optical scanning apparatus is fixed on the rear face of the auxiliary substrate from the surface side, and drive coil electrode terminals provided on the rear face of the optical scanning apparatus and the conductive pattern of the auxiliary substrate are electrically connected, while, above the mounting substrate on which a plurality of terminal pins are fitted through to the surface side thereof, the auxiliary substrate is fixed at a distance, with an intervening spacer, so that the protruding ends of the terminal pins on the surface side of the mounting substrate and the conductive pattern are electrically connected.
With such a construction, there is no need to form a cavity for allowing swinging movement of the movable portion of the optical scanning apparatus on the mounting substrate. Therefore it is possible to increase the strength of the mounting substrate.
Furthermore, in a sixth aspect, the construction may be such that the auxiliary substrate has a plurality of through holes in the periphery of the cavity, and has the conductive pattern for electrically connecting the surface side and the rear face side via the through holes, and the protruding ends of the terminal pins on the surface side of the mounting substrate are passed through the through holes of the auxiliary substrate to solder the terminal pins protruding from the surface side of the auxiliary substrate.